In recent years, so-called electronic music distribution (hereafter simply, “EMD”)—downloading digital music information available to the public on the Internet to a personal computer (hereafter simply, a “PC”) and reproducing the music information by a computer program in the PC—has attracted much attention.
In relation to this, techniques for delivering entertainment content complementary to a musical recording to a user's computer by means of a computer network link are disclosed in U.S. Pat. Nos. 5,987,525, 6,061,680, 6,154,773, and 6,161,132.
With the advent of the MP3 (MPEG audio layer-3) that is a CODEC enabling high-compression of digital music information while maintaining high-audio quality, users can easily compress and record, on their PCs, music information that is recorded on their music CDs in the Compact Disc Digital Audio (hereafter simply, “CD-DA”) format, using ripping software compliant with the MP3. The users can also store the music information in the hard disk unit of their PCs. Here, the ripping software is a computer program to convert music information recorded on music CDs into music information suitable for being handled on PCs. Furthermore, now that portable devices (hereafter simply, “PDs”) for reproducing music information compressed by the MP3, such as “RIO” manufactured by Diamond Multimedia Systems, Inc. have appeared, the users can write music information compressed by the MP3 into their PCs using a program for PCs, and play back music outside by taking the PCs there.
The MP3 has been widely accepted by the users and won enormous popularity for its convenience.
However, the high-compression feature of the MP3 suitable for data exchange on the Internet has created an increasing number of Websites publishing unauthorized data generated by the MP3 without permission of copyright holders of the data.
Predicting that CD sales will drop and the entire music industry will be on the decline in such a situation, the recording industry has established the SDMI (Secure Digital Music Initiative), a group defining a framework for distributing copyrighted music data on the Internet.
In such an effort, the following specific techniques are being employed. One technique is for embedding a digital watermark into music information to indicate that the music information is copyrighted content or not. Another technique is for encrypting compressed and recorded music information to prevent unauthorized copy from being made.